Method and apparatus for the collection of physiological electrical potentials

ABSTRACT

An invention is disclosed that provides an apparatus, method and system for the collection of physiological electrical potential signals. In one embodiment, the apparatus comprises integrating amplifier and an electrode into a combined unit for attaching or affixing to a subject (e.g., an animal or a human). Resulting from the extremely small or short connection between the conductive portion of the electrode and the amplifier, significantly less noise is introduced into the signal detected by the amplifier. The amplifier thus amplifies a signal with a much higher signal-to-noise ratio as compared with conventional electrode to lead wire to amplifier arrangements.

FIELD OF THE INVENTION

This invention relates to physiological electrical potentials and, moreparticularly, to a method and device for the collection of theseelectrical potentials.

BACKGROUND

Living animals generate electrical potentials which, when collected,detected and analysed, can be used for a variety of purposes. Forexample, synchronous neural activity in a live animal or human brainproduces electrical potentials that can be detected at the surface ofthe scalp with conductive electrodes. These detected potentials can thenbe used in a wide variety of clinical applications, particularlydiagnostic applications.

It is known to collect these electrical potentials generated by livinganimals through the application of passive electrodes applied to theskin of the animal. These electrodes consist of a conductive surface orpad that is coupled or adhered to the skin of a subject. The operationof the conductive pad is often facilitated by the additional applicationof a conductive substance, such as gel, between the skin and theelectrode. The conductive pad of the electrode is connected to a leadwire which, in turn, is electrically coupled to an amplifier. The lengthof the lead wire is typically in excess of 1 m (usually fromapproximately 1 m to 2.5 m) and electrically connects the amplifier(housed in a signal processing device) and the electrode. The amplifieramplifies the difference in electric potentials between a signalelectrode and a reference electrode, both of which are affixed to thesubject (human or animal). The amplifier is typically housed togetherwith some signal processing device which, typically, is also adapted torecord and analyse any detected electrical potentials which have beenamplified by the amplifier. Unfortunately, this known arrangement of theelectrode, lead wire and amplifier has significant shortcomings,particularly for the following reasons.

Unlike typically well known electrical potentials in common use in otherindustries and other areas of activity, the electrical potentialsgenerated by living animals are often very small in amplitude—often inthe millivolt, microvolt, or even nanovolt range. As a result, theseelectrical potentials are easily “drowned out” or lost due to noise fromthe electrical potentials generated by other items in the vicinity ofthe subject (e.g., lighting, the signal processing device, otherequipment, etc.). That is, the differential electric potentials ofinterest in most applications (often smaller than 1 microvolt) areusually smaller than the electrical noise that is detected by theamplifier when no signal is present.

Significant sources of electrical noise which will often be detected bythe amplifier are caused by the plurality of time-varying andtime-invariant electromagnetic fields that are often present in a testenvironment where the electrode-lead wire-amplifier arrangement isemployed. These time varying electromagnetic fields are inductively andcapacitively coupled to the lead wire that carries the signal from theelectrode to the amplifier. Consequently, these time varyingelectromagnetic fields introduce noise onto the lead wire that will bedetected and amplified by the amplifier. A second significant source ofnoise is motion artefacts; i.e., the noise induced in the lead wire asit moves through a static (i.e., time-invariant) electromagnetic field.

To address these known shortcomings, efforts have been made to shortenthe lead wire in an attempt to reduce noise. However, these efforts havehad limited success. Amongst the problems with these efforts is that itis impractical in many applications to tether a subject (whether it isan animal or human) with a wire that is less than about 1 meter long tothe amplifier.

Another measure to reduce noise that has had some success, albeitlimited, is achieved with differential measurements since common modenoise, i.e. noise that is identically present in two wires, can becancelled to a certain degree. Unfortunately, not all of the noiseinduced by the various electromagnetic fields is identical in bothsignal wires and, thus, some significant amount of noise will still benot cancelled and thus present in the recording system.

Additional efforts to reduce the effect of noise include conductingmultiple tests and then averaging the results of these multiple tests.Unfortunately, conducting repeated tests in an attempt to eliminate orreduce any noise detected has the unwanted effect of significantlylengthening the testing process. Since it is often preferred that thesubject remain still or, in some cases, unconscious, a lengthening ofthe testing process is quite undesirable especially when the testsubject is a young child or animal.

Another shortcoming with the known electrode-based systems of measuringelectrical potentials is the difficulty in determining whether theelectrodes have been properly attached or affixed to the subject (e.g.,animal or human), while proper attachment, as typically indicated by lowelectrical impedance between the electrodes, is crucial for the recordedsignal-to-noise ratio. As a result, significant care must be taken bythe clinician to properly attach these electrodes and then carefullymonitor any potentials measured to assess whether the measurements areindicative of improper electrode attachment. If a clinician or otheroperator is of the opinion that at least one of the electrodes isimproperly attached to the subject, a time consuming review of eachelectrode is necessary to determine which electrode is improperlyattached to the subject. To overcome this time consuming process someclinical systems include impedance detection, i.e., a means forautomatically detecting if an electrode is poorly connected with theskin of a subject. The accepted method of impedance detection (see forexample U.S. Pat. No. 5,368,041) is to introduce a small-current signalto each electrode. The voltage from each electrode to ground is measuredand is proportional to the impedance of the electrode. However, such animpedance-detection system requires additional circuitry and theintroduction of another electrical current. This additional current andcircuitry will be a further source of noise in any signal detected.Moreover, the additional circuitry increases the costs and complexity ofthe overall system.

Accordingly, a method and apparatus for the collection of electricalpotentials which addresses, at least in part, some of the above-notedshortcomings is desired.

SUMMARY OF THE INVENTION

In one aspect of the invention there is provided an apparatus comprisingan integrated amplifier and electrode into a combined unit for attachingor affixing to a subject (e.g., an animal or a human). Resulting fromthe extremely small or short connection between the conductive portionof an electrode and the amplifier, significantly less noise isintroduced into the signal detected by the amplifier. The amplifier thusamplifies a signal with a much higher signal-to-noise ratio as comparedwith conventional electrode to lead wire to amplifier arrangements.

In an alternate embodiment of the invention, an impedance detectionmethod and apparatus is provided that may be used whenever an amplifierwith bipolar transistor inputs is used to detect the signal (i.e., theelectrical potential generated by the subject). Bipolar transistoramplifiers, by their nature, introduce an input bias current into eachof the differential signal inputs. These bias currents are an inherentproperty of the bipolar transistor inputs and result in an offset at theamplifier output that is proportional to the difference in impedancebetween the input leads. The polarity or phase of the common-mode signalcan be used to determine which electrode contact is faulty, thusreducing the time-consuming and painstaking process that afflictscurrent electrode arrangements.

This method is ideally suited for applications where the signal ofinterest is a differential signal and advantageously requires noadditional circuitry to generate, filter, and detect the impedancesignal. Hence, it reduces the cost, size, complexity, and total noise ofthe system with compared current arrangements. A further advantage ofthese impedance-detection method and apparatus is that it isparticularly well suited for use in a small space, the type of physicalenvironment in which electrodes are often employed.

A further aspect of the invention provides a method and an apparatuscomprising mounting at least two signal electrodes to a subject and atleast one reference electrode. The at least one reference electrodecomprises a differential amplifier directly connected the conductiveportion of the at least one reference electrode. The at least twoelectrodes are each electrically connected to the differential amplifierof the at least one reference electrode via wires with the lengths closeto the distances between the connected electrodes.

As will be apparent to those of ordinary skill in the art, the methodsand apparatus achieve artefact noise reduction in at least three ways.First, at least one lead wire, a significant source of wire-inducednoise, is eliminated completely. Second, the remaining lead wires may beas short as allowed by the size of the area of interest on the subject(e.g., the distance between wires mounted to the subject's head) whichis typically much shorter than the typical one-meter length (or greater)used in known arrangements and systems. Third, motion artefacts aresignificantly reduced since all lead wires, electrodes and the amplifierare each mounted to the subject and all move together significantlyreducing differential movement and hence differential artefact noisethat otherwise would be induced in the lead wires due to motion throughenvironmental electromagnetic fields.

A further aspect of the invention comprises wireless transmission of theelectrical potentials amplified by the electrode-mounted amplifier(s) toa signal-processing device. In this aspect of the invention, theinvention further comprises electronic circuitry which transforms theamplified electrical potentials into radio waves and transmits them to aremote radio receiver.

In a still further aspect of the invention, the wireless transmission ofthe electrical potentials comprises performing some signal processingenabling wireless transmission of a digital representation of theamplified electrical potentials. A signal processing device is thenadapted to receive and use the digital representation of the amplifiedelectrical potentials transmitted from the subject.

In a still further aspect of the invention, an amplifier and relatedcircuitry comprise an integrated circuit affixed to an electrode thatemploys chip-on-board technology enabling the integrated circuit to bedirectly mounted to the conductive pad or a small printed circuit board(PCB). This arrangement results in a significantly smaller packagingthan conventional packaging (e.g., Small Outline Integrated Circuit(SOIC), etc.). The integrated circuit and its associated lead wireselectrically connected to the PCB may be encapsulated for itsprotection, for example in an epoxy resin.

In one aspect of the present invention there is provided an electrodemodule for affixing to a subject to assist in measuring electricalpotentials in said subject, said electrode module comprising anamplifier component mounted directly to an electrode.

In a further aspect of the invention there is provided a method ofamplifying electrical potentials in a subject, said method comprisingamplifying a differential electrical potential signal received fromfirst and second signal electrodes, said amplifying is performed near oron one of said signal electrodes and a reference electrode.

In a still further aspect of the invention there is provided a systemfor measuring electrical potentials in a subject, said system comprisinga pair of electrodes electrically coupled to an amplifier mounted to areference electrode, said reference electrode comprising a conductivepad electrically connected to said amplifier, said amplifier foramplifying a differential electrical signal detected by said pair ofelectrodes.

These as well as other novel advantages, details, embodiments, featuresand objects of the present invention will be apparent to those skilledin the art from following the detailed description of the invention, theattached claims and accompanying drawings, listed herein, which areuseful in explaining the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following text and drawings, wherein similar reference numeralsdenote similar elements throughout the several views thereof, thepresent invention is explained with reference to illustrativeembodiments, in which:

FIG. 1 is a side view schematic diagram depicting an embodiment of theinvention affixed to a subject's (human's) head;

FIG. 2 is top view schematic diagram of the embodiment of FIG. 1;

FIG. 3 is a schematic diagram of the reference electrode illustrated inFIGS. 1 and 2 embodying aspects of the present invention;

FIG. 4 is a more detailed diagram of the components of a portion of thereference electrode of FIG. 3;

FIGS. 5 and 6 are simplified circuit diagrams of the reference electrodeillustrated in FIG. 3; and

FIG. 7 is a side view schematic of an alternative embodiment of thepresent invention affixed to a subject's (human's) head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the described embodiments of the present invention, reference is madeto the subject from which electrical potentials are being detected,measured and analysed. The subject illustrated in some of the figures isillustrated as the head of a human. It is to be noted that other subjectareas (i.e., other portions of a human) or other animals could equallybe a subject for which the current invention could be employed to detectelectrical potentials.

Referencing FIG. 1, an electrical potential system 10 is illustrated.Electrical potential system 10 includes a reference electrode module 12(which, as is described below includes an amplifier component 38, notshown in FIG. 1) electrically coupled to two or more conventionalelectrodes 14. In FIG. 1, two signal electrodes 14 (also referred toherein as simply “electrodes 14”) are illustrated—a first electrode 14 ais illustrated in the foreground while a second electrode 14 b (shown indotted line) is in the background. Electrodes 14 a, 14 b areelectrically coupled to reference electrode module 12 by lead wires 20a, 20 b, respectively.

Reference electrode module 12 is also electrically coupled to signalprocessing device 18 by way of connector 16.

Reference electrode module 12 and electrodes 14 are affixed or mountedto subject 22 through known adhesives or other fixation methods ormechanisms. Additionally, a conductive substance such as electrode gel,for example, may be used to enhance or ensure electrical conductionbetween the skin of subject 22 and electrodes 12, 14.

Lead wires 20 a and 20 b are preferably selected to be taut whenelectrodes 12 and 14 have been affixed to subject 22. When lead wires 20a, 20 b are taut the chance of differential motion artefacts resultingfrom lead wire 20 a moving in a manner different from lead wire 20 b issignificantly reduced.

Connector 16 is preferably a conventional shielded wire allowingamplified electrical potential signals to be transmitted from referenceelectrode module 12 to signal-processing device 18.

Signal-processing device 18 operates to receive and process signalsreceived from reference electrode module 12 via connector 16. As will beapparent from the description below, signal-processing device 18 is aconventional signal-processing device that has been adapted to receiveamplified electrical potential signals rather than electrical potentialsthat have yet to be amplified. Signal-processing device 18 may include,for example, a visual display for displaying the received amplifiedsignals, a signal recorder component for recording the signal receivedfor later review and analysis, and various signal-processing circuitsand software for processing any amplified signals received. Such signalprocessing may include circuitry and software for further reducing anynoise contained in the received amplified signals. In alternativeembodiments, which are described in greater detail below, referenceelectrode module 12 and signal processing device 18 are adapted toassist an operator of system 10 to determine if an electrode 14 has beenpoorly affixed to subject 22.

Referencing FIG. 2, electrical potential system 10 is illustrated in atop view of subject 22. As noted above, lead wires 20 a, 20 b are tautlyand electrically connect electrodes 14 a, 14 b to reference electrodemodule 12.

Reference electrode module 12 is illustrated in greater in FIG. 3. Inthe exemplary embodiment, reference electrode module 12 includes aconventional electrode that has been adapted to include amplifiercomponent 38. Accordingly, reference electrode module 12 includesadhesive pad 34 that is used to affix electrode 12 to subject 22 andconductive pad 36 mounted to adhesive pad 34 for electrically connectingelectrode 12 to subject 22.

In some embodiments reference electrode module 12 may include or be usedin conjunction with a conventional conductive substance such as gel 32,for example, to assist in forming an electrical connection between theskin of subject 22 and conductive pad 36.

As known to those of ordinary skill in the art, conductive pad 36, whichis typically composed of silver, silver-plated tin, silver-chloride,gold or other conductive materials, is adapted to provide an electricalconnection between the subject 22 and, ultimately, signal processingdevice 18 (not shown in FIG. 3).

Electrically connected to conductive pad 36 is amplifier component 38.Amplifier component 38 is also adapted to be electrically connected tolead wires 20 a, 20 b and connector 16. Reference electrode module 12also acts as the reference electrical ground for electrodes 14 a and 14b.

Resulting from the inclusion of amplifier component 38 in referenceelectrode module 12, electrical potentials detected by electrodes 14will be passed into amplifier component 38 for signal amplification. Theuse of short lead wires 20 (usually less than 15-20 cm in length on anadult human's head and even shorter on an infant's or small animal'shead) results in far less noise being inductively or capacitivelycoupled to the lead wires that carries the signal from electrodes 14 tothe amplifier component 38 than conventional electrode-lead andwire-amplifier arrangements. Additionally, since lead wires 20 arepreferably taut, motion artifacts that induce noise in the lead wires 20as they move through static (i.e., time invariant) electromagneticfields are significantly reduced. The motion artifact noise issignificantly reduced compared to known arrangements since lead wires 20a and 20 b are likely to move through very similar paths and remainfixed relative to each other through these time-invariantelectromagnetic fields. Consequently, there is likely to be only verysmall differential potentials resulting from these differential motionartifacts that will be detected by amplifier component 38.

A schematic of the elements included in amplifier component 38 is shownin detail in FIG. 4. Amplifier component 38 includes, in the presentexemplary embodiment, a power supply 42, gain-setting resistor 48 andamplifier 44. Power supply 42 and gain-setting resistor 48 are bothelectrically connected to amplifier 44. Additionally, amplifier 44 iselectrically connected to connector 16 (which also connects tosignal-processing device 18—not shown in FIG. 4) and lead wires 20 a and20 b (which are also electrically connected to electrodes 14 a and 14 b,respectively and not shown in FIG. 4). Amplifier component 38 may alsoinclude optional protective coating 50 to provide physical protectionand additional electrical isolation of the various components. Epoxy orsilicone resins known in the art may be appropriate for such aprotective coating.

In the exemplary embodiment, amplifier 44 is an AD620 InstrumentationAmplifier available from Analog Devices of Norwood, Mass., USA (the datasheet for which is available from Analog Devices' web site athttp://www.analog.com/UploadedFiles/Data_Sheets/37793330023930AD620_e.pdf,the contents of which are hereby incorporated herein by reference).Alternative embodiments may employ different amplifiers. For example, itis believed that the INA128 or INA129 amplifier from the Burr-BrownCorporation (part of Texas Instruments) of Tucson, Ariz., USA may beappropriate in some circumstances. As persons of ordinary skill in theart will appreciate, other amplifiers that could be employed inalternative embodiments will have different pin-outs resulting inslightly differing wiring from that illustrated in FIG. 4.

In the exemplary embodiment, the AD620 amplifier (amplifier 44) has itsgain adjusted through use of different levels of resistance (RG) betweenpins 1 and 8. A single resistor 48 connected between these pins can beused to set the level of gain (G) of amplifier 44. In the exemplaryembodiment, gain is determined in accordance with equation (1) (whereR_(I) is internal resistance of amplifier 44 and is approximately 49.4kΩ for the AD620 amplifier):G=1+R_(I)/R_(G)  (1)

Resistor 48 may be a variable resistor or circuitry allowing for anoperator to vary the level of resistance presented to amplifier 44 thusallowing for the modification of the level of gain applied to anydifferential potentials detected by amplifier 44. Typically, manyoperating environments will require a level of gain (G) exceeding 100and preferably closer to 1000 (the maximum level of gain offered by theAD620 amplifier). Accordingly, resistor 48 would, in the exemplaryembodiment, require a level of resistance between approximately 499.0Ωand 49.5 Ω.

Power supply 42, which can be provided through use of a conventional(although preferably small) battery and any required and relatedcircuitry known to those of ordinary skill in the art, is electricallyconnected to pins 4 and 6 of amplifier 44.

Lead wires 20 a and 20 b are electrically connected to pins 2 and 3 ofamplifier 44.

Pin 8 of amplifier 44 is electrically connected to conductive pad 36(FIG. 3) of reference electrode module 12. As a result of the electricalconnection between amplifier 44 and conductive pad 36 (which, in turn,is connected to subject 22 during use), amplifier 44 will be providedwith a reference electrical ground.

Referencing FIGS. 1-4, in operation of system 10, an operator affixesreference electrode module 12 and electrodes 14 to a subject in therelevant areas of interest in a manner known to those of ordinary skillin the art. The operator also electrically connects, by way of a leadwire 20, each electrode 14 to reference electrode module 12. In theexemplary embodiment, electrode 14 a is connected to reference electrodemodule 12 by way of lead wire 20 a and electrode 14 b is connected toreference electrode module 12 by way of lead wire 20 b. Lead wires 20may be connected to electrodes 12, 14 prior or after fixation to thesubject. As noted above, it is preferable that once electrodes 12, 14have been affixed and lead wires 20 have been connected thereto, leadwires 20 are relatively taut. An operator also electrically connectsreference electrode module 12 to signal processing device 18 by way ofconnector 16.

Amplifier 44, powered by power supply 42, will begin to detectdifferential electrical potential signals presented by electrodes 14 aand 14 b. Amplifier 44 then amplifies these detected signals by the setlevel of gain (G)—where, as noted above, the level of gain (G) isdetermined by resistor 48 and the inner components of amplifier 44.Since lead wires 20 a, 20 b connecting electrodes 14 a, 14 b toamplifier 44 are considerably shorter than the lead wires in knownarrangements (i.e., 20 cm vs. 100-250 cm), the amount of electricalnoise inductively or capacitively coupled to the lead wires issignificantly reduced. Accordingly, amplifier 44 is presented withelectrical signals having a much greater (i.e., improved) signal tonoise ratio than in known arrangements. Additionally, since lead wires20 a, 20 b are substantially fixed relative to each other (especially,if lead wires 20 a and 20 b are taut), motion artifacts created by themovement of lead wires along different physical paths throughelectromagnetic fields (a source of considerable noise in known systems)are also significantly reduced.

Once electrical potentials detected by amplifier 44 have been amplified(resulting in an amplified signal having considerably less noise thanknown systems), the amplified signal is transmitted to signal processingdevice 18 via connector 16. The amplified signal can then be furtherprocessed, recorded and analysed to provide the required diagnostic testbeing performed on subject 22.

As will be appreciated by those of ordinary skill in the art, theresulting significant reduction in noise presented to the amplifier ofsystem 10 results in a reduction of signal processing that needs to beperformed to eliminate or reduce noise in any signal detected ascompared to known systems. Consequently, time averaging techniques whichare presently employed to reduce the effects of noise in a detectedsignal and which require multiple and/or lengthy tests to be conductedmay be reduced in many cases.

An exemplary simplified circuit diagram for system 10 is illustrated inFIGS. 5 and 6. Resulting from the arrangement and the selection of thecomponents therein, system 10 can also be used to assist in determiningif one of electrodes 14 a or 14 b, has become detached from subject 22and, if so, provide assistance in determining which one of theelectrodes has become so detached. System 10 includes an impedancedetection that may be used whenever an amplifier with bipolar transistorinputs (e.g., the AD620 amplifier described above) is used to detect thesignal (i.e., the electrical potential generated by the subject). Asthose of ordinary skill in the art will appreciate, a bipolar transistoramplifier will introduce an input bias current into each of thedifferential signal inputs. These bias currents are an inherent propertyof the bipolar transistor inputs and result in an offset at theamplifier output that is proportional to the difference in impedancebetween the input leads (e.g., the impedance presented by the leadwire-electrode-subject arrangement). Adapting signal-processing device18 to determine the polarity or phase of the common-mode signal,signal-processing device 18 can be used to determine which electrodecontact is faulty thus reducing the time-consuming and painstakingprocess that afflicts current electrode arrangements. An operator wouldthen be presented with some form of sensory feedback or signalindicating which one of the electrodes 14 has a faulty or poorconnection to subject 22. The sensory feedback presented to the operatormay be one or more of the following: a visual signal or indicator (e.g.,a text and/or graphical message), an audible signal (e.g., a warningbuzzer with, for example, different tones and/or volumes to indicatewhich electrode has a poor/faulty connection), and/or a tactile or othersense of touch signal (e.g., a vibration generated by a device—such as,for example, a pager-like device—worn by operator, with different typesof vibrations associated with each of electrodes 14). In the preferredembodiment, the sensory signal is a combination of an audible alarm orwarning coupled with a visual signal output on a display screen formingpart of signal-processing device 18. The audible alarm provides anindication that one of the electrodes 14 has a poor or faulty connectionto subject 22 and prompts the operator to review the display screen ofsignal-processing device 18. The visual indicator displayed bysignal-processing device 18 provides to the operator data (text and/orgraphics) indicating which one of the electrodes 14 is the source of theproblem.

Referring to FIG. 6, Z₁ represents the impedance presented to amplifier44 by the connection between the subject 22 and electrode 14 a and Z₂represents the impedance presented to amplifier 44 by the connectionbetween subject 22 and electrode 14 b. The bias current flowing throughthe subject-electrode connections is represented by i_(offset1) andi_(offset2), respectively. The offset voltage (V_(offset)) followsequation (2) set out below:((i _(offset1) −i _(offset2))(Z ₁ −Z ₂)G)=V _(offset)  (2)If the impedances of the subject-electrode connections are the same orsimilar (i.e., both are well adhered or affixed to the subject) thesecond term of equation (2) will be zero or very small resulting in avery small offset voltage. If one of the two electrodes is poorlyaffixed to subject 22 (or has become disconnected), then the offsetvoltage will be relatively large. If electrode 14 a is disconnectedV_(offset) will be much greater than zero and this value can bedisplayed (or some other signal generated) to an operator of system 10by signal processing device 18. Consequently, the operator of system 10will be provided information identifying the electrode which has beenpoorly connected or affixed to subject 22 saving considerable time andeffort that would otherwise be expended. Similarly, if V_(offset) ismuch less than zero, this value is indicative of electrode 14 b beingdisconnected or poorly connected to subject 22 and the operator can beinformed of this situation. As a result of this operation of system 10,an operator of system 10 can spend much less time making a determinationof which of the electrodes needs to be re-attached or better attached tosubject 22.

As will be appreciated, in alternative embodiments of the presentinvention having multiple pairs of electrodes 14 affixed to a subject,the assistance provided to an operator of system 10 in determining whichelectrodes 14 have been poorly attached to the subject will result insignificant time and cost savings.

This advantage of the present invention is suitable for applicationswhere the signal of interest is a differential signal. Beneficially,such an advantage requires no additional circuitry to generate, filterand detect the impedance signal and results in a reduction of the cost,size, complexity, and total noise of the system compared currentarrangements. A further advantage of the impedance detection method andapparatus is that it is particularly well suited for use in a smallspace; the type of physical environment in which electrodes are oftenemployed.

Some alternatives to the exemplary embodiment illustrated as system 10will now be described.

In one alternative embodiment, system 10 is adapted to transmitamplified signals from the subject to signal processing device 18 usinga wireless connection as illustrated by system 70 in FIG. 7. Similar tosystem 10 (FIG. 1), system 70 includes a pair of conventional electrodes14 a, 14 b electrically connected by way of lead wires 20 a, 20 b,respectively, to reference electrode module 12. Reference electrodemodule 12, which also includes the amplifier component 38 describedabove, is electrically connected to connector 72 rather than connector16. Connector 72 electrically connects reference electrode module 12 tosignal transmitter 74.

Signal transmitter 74 is adapted to receive the detected and amplifiedsignals (as described above) processed by amplifier component mounted toreference electrode module 12. However, rather than transmit thedetected and amplified signal over a wire to signal-processing device 18like system 10 of FIG. 1, signal transmitter 74 transmits the signal viaradio waves to signal-processing device 18. In turn, signal processingdevice 18 has been adapted to receive the transmitted radio signal byinclusion of radio-receiving device and antenna 76. Those of ordinaryskill in the art will appreciate that signal transmitter 74 willmodulate (either in the amplitude or frequency domains, or both) a radiosignal of selected frequency and, thus, will include circuitry and powersources (e.g., a battery) to perform this function. Additionally, signaltransmitter 74 may include some filtering circuitry to remove some ofthe unwanted (although limited) noise included in the amplified signalgenerated by reference electrode module 12.

In a further alternative, signal transmitter 74 may transmit a digitalrepresentation of the amplified signal generated by reference electrodemodule 12. In this alternative embodiment, signal transmitter wouldinclude a conventional analog-to-digital processor (A/D). The digitalrepresentation could then be transmitted using known wirelesstransmission protocols (e.g., BlueTooth, 802.11a, b or g, or the like).In this instance, receiving device and antenna 76 would also requiresome modification so that the digitally transmitted signal can bereceived and processed as required.

While the preferred embodiment includes the amplifier component mounteddirectly on the underlying electrode, a further alternative embodimentincludes the amplifier component affixed to subject 22 and near to theunderlying electrode (i.e., near to conductive pad 36 of referenceelectrode module 12). For example, amplifier component could be includedin the circuitry of signal transmitter 74 (FIG. 7).

In a still further alternative embodiment, the amplifier component ismounted on or near a signal electrode (rather than mounting theamplifier component on or near the reference electrode) to form anelectrode module.

In view of the many possible embodiments to which the principles of thisinvention may be applied, it should be recognized that the embodimentsdescribed herein and shown in the drawing figures is meant to beillustrative only and should not be taken as limiting the scope ofinvention. For example, those of skill in the art will recognize thatthe elements of the illustrated embodiment can be modified inarrangement and detail without departing from the spirit of theinvention. Therefore, the invention as described herein contemplates allsuch embodiments as may come within the scope of the following claimsand equivalents thereof.

1. An electrode module for affixing to a subject to assist in measuringelectrical potentials in said subject, said electrode module comprisingan amplifier component mounted directly to an electrode.
 2. Theelectrode module of claim 1 wherein said electrode comprises a referenceelectrode.
 3. The electrode module of claim 1 wherein said amplifiercomponent comprises an amplifier adapted to amplify an electrical signalreceived from one or more signal electrodes.
 4. The electrode module ofclaim 2 wherein said amplifier component is further adapted to transmitan amplified signal to a signal-processing device.
 5. The electrodemodule of claim 2 wherein said amplifier component is further adapted totransmit said an amplified signal to a signal-processing device via awireless connection.
 6. The electrode module of claim 5 wherein saidamplifier component further comprises a wireless signal transmitter,said wireless signal transmitter adapted to wirelessly transmit saidamplified electrical signal to a signal-processing device.
 7. Theelectrode module of claim 6 wherein said wireless signal transmittercomprises a radio frequency modulator.
 8. The electrode module of claim6 wherein said wireless signal transmitter further comprises filtercircuitry for filtering electrical signals received from said one ormore signal electrodes.
 9. The electrode module of claim 8 wherein saidfilter circuitry filters said amplified electrical signal.
 10. Theelectrode module of claim 6 wherein said wireless signal transmitter isadapted to transmit a digital representation of said amplifiedelectrical signal to a signal-processing device.
 11. The electrodemodule of claim 9 wherein said wireless signal transmitter transmitssaid digital representation using a wireless transmission protocol. 12.The electrode module of claim 2 wherein said amplifier comprises adifferential signal amplifier adapted to amplify electrical signalsreceived from said one or more signal electrodes.
 13. The electrodemodule of claim 2 wherein said amplifier comprises bipolar transistorinputs.
 14. The electrode module of claim 2 wherein said one or moresignal electrodes comprises a first signal electrode and a second signalelectrode and wherein said amplifier, when one of said first or saidsecond signal electrode is poorly connected to, or detached from, asubject, is further adapted to transmit a signal indicating which ofsaid first or said second signal electrode is poorly connected to, ordetached from, said subject.
 15. The electrode module of claim 14wherein said amplifier comprises a bipolar transistor amplifier, saidbipolar transistor amplifier introducing a bias current into the signalsreceived from said first and second signal electrodes.
 16. The electrodemodule of claim 15 wherein said bipolar transistor amplifier generatesan output proportional to the difference between the impedance presentedto said bipolar transistor amplifier by said first and second signalelectrodes; and wherein said signal indicating which of said first orsaid second signal electrode is poorly connected to, or detached from,said subject comprises a signal based upon said output proportional tothe difference in impedance presented to said bipolar transistoramplifier.
 17. The electrode module of claim 16 wherein said signalindicating which of said first or said second signal electrode is poorlyconnected to, or detached from, said subject comprises at least one of avisual signal, an audible signal and a tactile signal, said signal forpresentation to an operator by a signal processing device.
 18. Theelectrode module of claim 14 wherein said signal indicating which ofsaid first or said second signal electrode is poorly connected to, ordetached from, said subject comprises a sensory signal for presentationto an operator.
 19. A method of amplifying electrical potentials in asubject, said method comprising amplifying a differential electricalpotential signal received from first and second signal electrodes, saidamplifying is performed near or on one of: said signal electrodes and areference electrode.
 20. The method of claim 19 wherein said amplifyingis performed by a reference electrode module and said referenceelectrode module comprises an amplifier mounted and electricallyconnected to a reference electrode, said reference electrode defining azero output voltage for said amplifier.
 21. The method of claim 20wherein said reference electrode module is affixed to a subject andwherein said first and second signal electrodes are electricallyconnected to inputs of said amplifier.
 22. The method of claim 21further comprising transmitting said amplified differential electricalpotential signal to a signal-processing device.
 23. The method of claim22 wherein said transmitting comprises transmitting said amplifieddifferential electrical potential signal to said signal-processingdevice via a wireless connection.
 24. The method of claim 23 whereinsaid transmitting comprises generating a modulated radio frequencysignal representative of said amplified differential electricalpotential signal.
 25. The method of claim 23 further comprises prior tosaid transmitting generating a digital representation of said amplifieddifferential electrical potential signal.
 26. The method of claim 22further comprising, in the event that one of said first and secondsignal electrodes is poorly affixed to, or detached from, a subject,presenting to an operator a sensory signal indicating which one of saidfirst and second signal electrodes is poorly affixed to, or detachedfrom, said subject.
 27. The method of claim 26 wherein said sensorysignal comprises at least one of: a visual signal; an audible signal;and a tactile signal.
 28. The method of claim 26 wherein said presentingto an operator at least one of a visual and audible signal comprisesgenerating said at least one of a visual and audible signal responsiveto the difference in impedance presented by said first and second signalelectrodes to said amplifier.
 29. The method of claim 28 wherein saidgenerating comprises introducing a bias current into said inputsreceived from said first and second signal electrodes.
 30. The method ofclaim 28 wherein said amplifier comprises a bipolar transistoramplifier.
 31. A system for measuring electrical potentials in asubject, said system comprising a pair of electrodes electricallycoupled to an amplifier mounted to a reference electrode, said referenceelectrode comprising a conductive pad electrically connected to saidamplifier, said amplifier for amplifying a differential electricalsignal detected by said pair of electrodes.
 32. The system of claim 31wherein said amplifier comprises a bipolar transistor amplifier.
 33. Thesystem of claim 32, in the event that one of said pair of electrodes ispoorly affixed to, or detached from a subject, said amplifier adapted togenerate a signal indicating which one of said pair of electrodes ispoorly affixed to, or detached from, said subject.
 34. The system ofclaim 33 wherein said signal indicating which one of said pair ofelectrodes is poorly affixed to, or detached from, said subjectcomprises a sensory signal for presentation to an operator, said sensorysignal comprising at least one of: a visual signal; an audible signal;and a tactile signal.
 35. The system of claim 31 further comprising aconnector electrically connecting an output of said amplifier to asignal-processing device.
 36. The system of claim 35 wherein saidconnector comprises a wireless transmitter for wirelessly transmittingthe output of said amplifier to a signal-processing device.
 37. Thesystem of claim 31 wherein said wireless transmitter further comprisesan analog-to-digital processor for generating a digital representationof the output of said amplifier and wherein said wireless transmittertransmits said digital representation to a signal-processing device. 38.The system of claim 31 further comprises filtering circuitry, saidfiltering circuitry adapted to filter out noise from said differentialelectrical signal detected by said electrodes.
 39. The system of claim38 further comprises filtering circuitry, said filtering circuitryadapted to filter out noise from said amplified differential electrical.